When it comes to understanding the meaning of the phrase "not on", there are a variety of synonyms that can be helpful. For example, alternatives include "off", "disconnected", "inactive", and "disabled". Each of these words provides a slightly different nuance or context for the phrase, but generally all refer to a state of not being operational or present. In addition to these synonyms, other useful phrases to convey the opposite of "on" might include "not in use", "offline", "out of service", or simply "not active". Depending on the specific context, any of these synonyms might be more or less appropriate for aiding in communication or understanding.